Great insights @elliottbnewcombjr . I especially like this quote from praeclara.org:
"Why then did Handel compose Messiah? Or more precisely, why did he dare? The immediate answer is that by 1741 Handel’s life and career were in trouble. Not only was he deeply in debt and partially paralyzed by stroke, but his latest Old Testament oratorios, including Israel in Egypt, had been poorly received. When the Duke of Devonshire invited him to compose a work for a concert in Dublin to raise money for a variety of charities (including the Charitable Musical Society for the Relief of Imprisoned Debtors), Handel most likely decided upon Messiah in the belief that an oratorio based on “new material”� — the New Testament — might succeed where his previous oratorios had failed and that perhaps the concert’s Christian charitable purpose would shield him from charges of committing sacrilege.
Even then, Handel took extra precautions. Although Messiah is about the life and passion of Jesus, more than half its texts derive from the Old Testament."
and, "Handel’s own attitudes toward Messiah remain a mystery, and we will probably never know if he intended this work as a clever career move or as a tribute to God, or, as is quite possible, both."